Display device

ABSTRACT

In a capacitive touch panel, edge regions of the panel display generally have poor accuracy of coordinate detection of a touch point as compared to the intermediate region of the panel display. A display device includes a plurality of first electrodes arranged at predetermined pitches and extending in a X-direction; and a plurality of second electrodes arranged at predetermined pitches and extending in a Y-direction, wherein both endmost first electrodes of the plurality of first electrodes have a smaller pitch than the other first electrodes, both endmost second electrodes of the plurality of second electrodes have a smaller pitch than the other second electrodes, and the display device is configured to detect a touch based on a capacitance variation at one or more of intersections of the plurality of first electrodes with the plurality of second electrodes.

CLAIM OF PRIORITY

The present application claims priority from Japanese patent applicationJP2013-144385 filed on Jul. 10, 2013, the content of which is herebyincorporated by reference into this application.

BACKGROUND

The present disclosure relates to display devices and is applicable to,for example, display devices with touch panels.

A liquid crystal display device includes a liquid crystal display panel,wherein the liquid crystal display panel is formed by enclosing a liquidcrystal composition between a pair of substrates. Meanwhile, variousdisplay devices have been mass-produced in which a touch panel isdisposed as an input device at the front of a liquid crystal displaypanel. In order to detect an input (hereinafter referred to as a touch)to the touch panel, a technique using a variation in capacitance orresistance is proposed.

A touch panel of a type in which a capacitance variation can be detectedis, specifically, a touch panel configured to detect a variation in thecapacitance between a pair of electrodes disposed with an insulatingfilm in between and is hereinafter referred to as a capacitive touchpanel. Capacitive touch panels are classified into an external typeprovided outside the display panel (see, for example, JP-A-2003-511799or its corresponding U.S. Pat. No. 7,030,860) and a built-in typeprovided inside the display panel. An example of the built-in typecapacitive touch panel is a so-called in-cell display panel in whicheach of common electrodes (counter electrodes) for image displaypreviously provided in the display panel is also used as one of a pairof electrodes for a touch sensor and the other electrode (touchdetection electrode) of the pair is disposed crosswise with respect tothe common electrode (see, for example, JP-A-2009-244958 or itscorresponding US Patent Application No. 2010/0182273).

SUMMARY

The inventors conducted various studies on the capacitive touch paneland have found the following problem.

Specifically, in the capacitive touch panel, edge regions of the paneldisplay have poor accuracy of coordinate detection of a touch point ascompared to the intermediate region of the panel display.

A brief description will be given below of a summary of a representativeone of aspects according to the present disclosure.

In a display device, endmost detection electrodes of a panel display ofa touch panel are arranged at a smaller pitch than the other detectionelectrodes thereof.

With the aforementioned display device, the accuracy of coordinatedetection in the edge regions of the panel display can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a basic structure of a liquid crystaldisplay device according to Embodiment 1.

FIG. 2 is a schematic view showing a basic structure of a liquid crystaldisplay panel according to Embodiment 1.

FIG. 3 is an enlarged schematic cross-sectional view showing a portionof a cross section of a display according to Embodiment 1.

FIG. 4A is a plan view of a combination of a transmitting electrodepattern and a receiving electrode pattern according to ComparativeExample 1.

FIG. 4B is a plan view of a combination of a transmitting electrodepattern and a receiving electrode pattern according to Embodiment 1.

FIG. 4C is a plan view of another combination of a transmittingelectrode pattern and a receiving electrode pattern according toEmbodiment 1.

FIG. 4D is a plan view of still another combination of a transmittingelectrode pattern and a receiving electrode pattern according toEmbodiment 1.

FIG. 5 is a view showing touch responses at a central point of thepanel.

FIG. 6 is a view showing touch responses at a near-edge point of thepanel according to Comparative Example 1.

FIG. 7A is a view showing touch responses at an edge point of the panelaccording to Comparative Example 1.

FIG. 7B is a view showing touch responses at a near-edge point of thepanel according to Comparative Example 1.

FIG. 7C is a view showing touch responses at another near-edge point ofthe panel according to Comparative Example 1.

FIG. 8A is a view showing touch responses at an edge point of the panelaccording to Embodiment 1.

FIG. 8B is a view showing touch responses at a near-edge point of thepanel according to Embodiment 1.

FIG. 8C is a view showing touch responses at another near-edge point ofthe panel according to Embodiment 1.

FIG. 9 is a flowchart of sensitivity correction according to Embodiment1.

FIG. 10A is a diagram for illustrating a peripheral coordinatecorrection according to Comparative Example 1.

FIG. 10B is a diagram for illustrating a peripheral coordinatecorrection according to Embodiment 1.

FIG. 11 is a diagram showing a basic structure of a touch detectioncircuit.

FIG. 12A to 12D are diagrams showing signal waveforms of the touchdetection circuit.

FIG. 13 is a diagram showing a basic structure of a touch detectioncircuit having a calibration function.

FIG. 14 is a flowchart of a calibration according to Embodiment 1.

FIG. 15 is a block diagram showing a general structure of a touch paneldevice according to Embodiment 2.

FIG. 16 is a schematic cross-sectional view showing a cross-sectionalstructure of a touch panel in Embodiment 2.

FIG. 17A is a plan view of a combination of a transmitting electrodepattern and a receiving electrode pattern according to ComparativeExample 2.

FIG. 17B is a plan view of a combination of a transmitting electrodepattern and a receiving electrode pattern according to Embodiment 2.

FIG. 17C is a plan view of another combination of a transmittingelectrode pattern and a receiving electrode pattern according toEmbodiment 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a description will be given of embodiments with referenceto the drawings. Note that in all the drawings for illustrating theembodiments elements having the same functions are designated by thesame reference characters and a description thereof will not berepeated.

Although in the following embodiments a display device will be describedtaking as an example a liquid crystal display device, the presentdisclosure is applicable to display devices of other types, such as anorganic EL display device.

Embodiment 1

FIG. 1 is a schematic view showing a basic structure of a liquid crystaldisplay device according to Embodiment 1. As shown in this figure, aliquid crystal display device 100 includes a liquid crystal displaypanel 1, a drive circuit 5, a flexible substrate 70, a front panel 40, astorage case (not shown), and a backlight (not shown).

The liquid crystal display panel 1 is formed by overlaying a TFTsubstrate (first substrate) 2 and a color filter substrate (secondsubstrate) 3 at a predetermined distance from each other, bondingtogether both the substrates via a sealing material (not shown) placedin a frame shape between both the substrates along the peripheral edgesof the substrates, filling a space within the frame-shaped sealingmaterial with a liquid crystal composition, encapsulating the liquidcrystal composition, and then attaching polarizing plates on the outsidesurfaces of both the substrates.

The TFT substrate 2 is provided with a plurality of counter electrodes21 and a plurality of counter electrode signal lines 22 each connectingbetween the drive circuit 5 and an associated one of the plurality ofcounter electrodes 21. Thus, a counter electrode signal is transmittedfrom the drive circuit 5 through the counter electrode signal lines 22to the counter electrodes 21. The color filter substrate 3 is providedwith a plurality of detection electrodes 31. The detection electrodes 31are connected at a connecting part 77 with a flexible substrate 75. Theflexible substrate 75 is connected at a connector 80 with a flexiblesubstrate 70. A detection signal from each detection electrode 31 istransmitted through the flexible substrate 75, the connector 80, and theflexible substrate 70 to the drive circuit 5.

The liquid crystal display panel 1 includes a display (to be describedhereinafter in detail) including multiple pixels arranged in a matrix.The counter electrodes 21 constitute a common electrode and are disposedon the TFT substrate 2 to face pixel electrodes forming the pixelstogether with the counter electrodes 21. Specifically, the liquidcrystal display panel 1 is of a lateral electric field type, such as FFS(fringe field switching) or IPS (in-plane switching). When a voltage isapplied between both the electrodes forming each pixel, the orientationof liquid crystal molecules in the pixel changes. The proportion oflight transmitting through the panel changes with the change in theorientation of liquid crystal molecules, so that an image is displayed.

Next, a description will be given of the counter electrodes 21 and thedetection electrodes 31 with reference to FIG. 2. Although, as describedpreviously, the counter electrodes 21 constitute a common electrodeprovided on the TFT substrate 2, they are constructed by dividing thecommon electrode into a plurality of sections as shown in FIG. 2 so thatthey can be used as drive electrodes for detecting a touch. A counterelectrode signal is supplied from the drive circuit 5 to the counterelectrodes 21. Although the counter electrode signal applied to thecounter electrodes 21 is mainly a voltage for the common electrode, adrive signal for use in detecting a touch is applied thereto with atiming when writing to the pixels is not performed.

When the drive signal is applied to the counter electrodes 21, thedetection electrodes 31 disposed at a certain distance from the counterelectrodes 21 and forming capacitors with the counter electrodes 21generate detection signals. The detection signals are extracted throughdetection electrode terminals 36 to the outside.

Dummy electrodes 33 are formed on both sides of each detection electrode31. The dummy electrodes 33 are connected neither to any electrode norto any line. Each detection electrode 31 is extended at one end towardthe adjacent two dummy electrodes 33 to form a T-shaped detectionelectrode terminal 36. The TFT substrate 2 has, in addition to thecounter electrode signal lines 22, various lines and terminals formedthereon, such as drive circuit input terminals 25.

FIG. 3 shows an enlarged schematic cross-sectional view of a portion ofa cross section of the display. As shown in FIG. 3, the TFT substrate 2is provided with a pixel section 200, in which the counter electrodes 21form elements of pixels and are used for displaying an image.Furthermore, a liquid crystal composition (liquid crystal layer) 4 issandwiched between the TFT substrate 2 and the color filter substrate 3.The detection electrodes 31 provided on the color filter substrate 3 andthe counter electrodes 21 provided on the TFT substrate 2 formcapacitors. Thus, when a drive signal is applied to the counterelectrodes 21, the voltages of the detection electrodes 31 change. Whenat this time a conductor, such as a finger 108, comes close to ortouches any one of the detection electrodes 31 through the front panel40 as shown in FIG. 3, the capacitance between the detection electrode31 and the associated counter electrode 21 changes, so that the voltagegenerated in the detection electrode 31 also changes as compared tobefore the conductor comes close to or touches it.

By detecting the capacitance variation occurring between the pair ofcounter electrode 21 and detection electrode 31 formed in the liquidcrystal display panel 1, the liquid crystal display panel 1 can functionas a touch panel.

FIGS. 4A to 4D are views schematically showing plane patterns ofelectrodes of a capacitive in-cell touch panel. For convenience ofdescription, these figures show the case where the touch panel includesseven counter electrodes (transmitting electrodes, Tx electrodes orfirst electrodes) 21 and five detection electrodes (receivingelectrodes, Rx electrodes or second electrodes) 31. FIG. 4A shows anordinary electrode pattern (Comparative Example 1), FIG. 4B shows afirst example of this embodiment where the pitch of the endmostelectrodes is changed from that in the ordinary electrode pattern (theelectrode pattern is tailored in edge regions), FIG. 4C shows a secondexample of this embodiment where the pitch of the endmost electrodes ischanged (edge regions of the electrode pattern are simply cut), and FIG.4D is a third example of this embodiment where the pitch of the endmostelectrodes is changed (the electrode pattern is proportionally reducedin edge regions).

In Comparative Example 1 of FIG. 4A, all the Tx electrodes 21 have equalwidths and equal spacings and all the Rx electrodes 31 also have equalwidths and equal spacings. The width of each Tx electrode 21 is greaterthan the spacing between each pair of adjacent Tx electrodes 21, whilethe width of each Rx electrode 31 is smaller than the spacing betweeneach pair of adjacent Rx electrodes 31. The pitch (P_(Tx)) of each Txelectrode 21 is the distance between the pair of adjacent horizontalbroken lines. All the pitches (P_(Tx)) of the Tx electrodes 21 areequal. The pitch (P_(Rx)) of each Rx electrode 31 is the distancebetween the pair of adjacent vertical broken lines. All the pitches(P_(Rx)) of the Rx electrodes 31 are equal. Each Tx electrode 21 islocated in the middle between the pair of adjacent horizontal brokenlines, while each Rx electrode 31 is located in the middle between thepair of adjacent vertical lines.

In the first example of FIG. 4B where the pitch of the endmostelectrodes is changed, the width of the endmost Tx electrodes (Tx1, Tx7)21 ₁, 21 ₇ is smaller than the width of the other Tx electrodes 21 andthe pitch (P_(Txe)) of the endmost Tx electrodes (Tx1, Tx7) 21 ₁, 21 ₇is smaller than the pitch (P_(Tx)) of the other Tx electrodes 21 (i.e.,P_(Txe)<P_(Tx)). Furthermore, the pitch (P_(RXe)) of the endmost Rxelectrodes (Rx1, Rx5) 31 ₁, 31 ₅ is smaller than the pitch (P_(Rx)) ofthe other Rx electrodes 31 (i.e., P_(RXe)<P_(Rx)). The distance fromeach endmost Rx electrode (Rx1, Rx5) 31 ₁, 31 ₅ to the ends of theintersecting Tx electrodes in the X-direction is reduced. In otherwords, the endmost Rx electrodes (Rx1, Rx5) 31 ₁, 31 ₅ are offset fromthe middle between the pair of adjacent vertical broken lines towardsthe ends of the intersecting Tx electrodes in the X-direction. In thiscase, leaving the distance between each endmost Rx electrode (forexample, Rx1) and the adjacent Rx electrode (for example, Rx2) unchangedfrom the distance between the other pairs of adjacent Rx electrodes isan ingenuity of avoiding a change of sensitivity of the Rx electrode(Rx2) next to the endmost Rx electrode (Rx1). Furthermore, in proportionto the pitch reduction, the width of the endmost Rx electrodes 31 ₁, 31₅ is reduced. Although the pitch reduction may cause a deterioration inthe sensitivity of the endmost electrodes, the concurrent widthreduction of the endmost Rx electrodes 31 ₁, 31 ₅ reduces thesensitivity deterioration.

In the second example of FIG. 4C where the pitch of the endmostelectrodes is changed, the pattern of the endmost Tx electrodes and thepattern of the endmost Rx electrodes are simply cut. Although also inFIG. 4C the pitch (P_(Rxe)) of the endmost Rx electrodes 31 _(1C), 31_(5C) is smaller than the pitch (P_(Rx)) of the other Rx electrodes 31,FIG. 4C is different from FIG. 4B in that the width of the endmost Rxelectrodes 31 _(1C), 31 _(5C) is equal to the other Rx electrodes 31. Inthis case, the sensitivity is reduced as compared to the case of FIG. 4Bbut the coordinate accuracy can be effectively improved. The pitches andwidths of the Tx electrodes are the same as in FIG. 4B.

In the third example of FIG. 4D where the pitch of the endmostelectrodes is changed, the pattern of the endmost Tx electrodes and thepattern of the endmost Rx electrodes are proportionally reduced.Although also in FIG. 4D the pitch (P_(Rxe)) of the endmost Rxelectrodes is smaller than the pitch (P_(Rx)) of the other Rxelectrodes, FIG. 4D is different from FIG. 4B in the following point:since the regions of the endmost Rx electrodes 31 _(1D), 31 _(5D) areproportionally reduced, the distance between each endmost Rx electrode31 _(1D), 31 _(5D) and the adjacent Rx electrode 31 is different fromthe distance between the other pairs of adjacent Rx electrodes. In thiscase, the sensitivity of the electrodes next to the endmost electrodesis slightly reduced but the coordinate accuracy can be effectivelyimproved. Since the regions of the endmost Rx electrodes 31 _(1D), 31_(5D) are proportionally reduced, the width of the endmost Rx electrodes31 _(1D), 31 _(5D) is smaller than the width of the other Rx electrodes31 and each endmost Rx electrode (Rx1, Rx5) 31 _(1D), 31 _(5D) islocated in the middle between the pair of adjacent vertical brokenlines. The pitches and widths of the Tx electrodes are the same as inFIG. 4B.

<Principle of Coordinate Accuracy Improvement>

The reason why the coordinate accuracy is improved by reducing the pitchof the endmost electrodes is that the area where only one endmostelectrode responses to a touch on a near-edge point of the panel isreduced and a plurality of electrodes can response to the touch. Thiswill be described next.

A method commonly used to calculate the coordinate of a touch point isto reckon as a touch detection coordinate the centroid of some responsevalues to a touch on one or more of intersections of Tx electrodes withRx electrodes (Tx-Rx intersections). This method is also assumed for thepresent disclosure. For simplicity of description, the pitch (P_(Tx)) ofthe Tx electrodes and the pitch (P_(Rx)) of the Rx electrodes aresupposed to be equal to each other and the diameter (=2r) of a pseudofinger touching the panel is supposed to be also equal to the pitch ofthe electrodes. A difference of touches on near-edge points of the panelfrom touches on intermediate points of the panel is that no electrodeexists on one side of the touch point.

FIG. 5 is a view showing responses to a touch on a central point of thepanel. The upper diagram of FIG. 5 shows a touch point on the panel andthe lower diagram of FIG. 5 shows response values to the touch. As shownin the upper diagram of FIG. 5, the center of the pseudo finger FF islocated within Intersection 6 but the pseudo finger FF extends toIntersection 7. As shown in the lower diagram of FIG. 5, a touch on thecentral point of the panel provides significant responses atIntersection 6 and Intersection 7. Therefore, the center of the touchpoint can be accurately calculated using the aforementioned centroidcalculation. FIG. 6 is a view showing responses to a touch on anear-edge point of the panel according to Comparative Example 1. Theupper diagram of FIG. 6 shows a touch point on the panel and the lowerdiagram of FIG. 6 shows response values to the touch. As shown in theupper diagram of FIG. 6, the center of the pseudo finger FF is locatedwithin Intersection 4 but the pseudo finger FF extends beyond the edgeto the outside. As shown in the lower diagram of FIG. 6, a touch on thenear-edge point of the panel provides a significant response only atIntersection 4. Therefore, the detection accuracy in the horizontaldirection is poor. As described previously, each electrode is locatedbetween the adjacent broken lines.

This will be described more specifically with reference to FIGS. 7A to7C. FIG. 7A is a view showing responses to a touch on an edge point(x=0) of the panel according to Comparative Example 1. The upper diagramof FIG. 7A shows a touch point on the panel and the lower diagram ofFIG. 7A shows response values to the touch. As shown in the upperdiagram of FIG. 7A, the center of the pseudo finger FF is located at anedge (x=0) of the panel. As shown in the lower diagram of FIG. 7A, whenthe touch point is at x=0, only intersections (Intersections 2, 4, and6) of the electrode R×N respond. FIG. 7B is a view showing responses toa touch on a point (x=r/2) r/2 distant from an edge of the panelaccording to Comparative Example 1. The upper diagram of FIG. 7B shows atouch point on the panel and the lower diagram of FIG. 7B shows responsevalues to the touch. As shown in the upper diagram of FIG. 7B, thecenter of the pseudo finger FF is located at a near-edge point (x=r/2)of the panel. As shown in the lower diagram of FIG. 7B, when the touchpoint is at x=r/2, Intersection 3 slightly responds but its responselevel is not significantly different from a noise level, which does notcontribute to the coordinate calculation. As a result, in edge regionsof the panel, only one electrode R×N responds to touches on points fromx=0 to x=r/2, so that a difference in position in the X-direction cannotbe detected. In other words, in the range of touch points from x=0 tox=r/2, the position of the detected coordinate stays unchanged. This isthe reason why the coordinate accuracy in the edge regions of the panelbecomes poor. FIG. 7C is a view showing responses to a touch on a point(x=r) r distant from an edge of the panel according to ComparativeExample 1. The upper diagram of FIG. 7C shows a touch point on the paneland the lower diagram of FIG. 7C shows response values to the touch. Asshown in the upper diagram of FIG. 7C, the center of the pseudo fingerFF is located at a near-edge point (x=r) of the panel. As shown in thelower diagram of FIG. 7C, when the touch point is at x-r, Intersection 3provides a sufficiently significant response value, which contributes tothe coordinate calculation.

Touch responses in the case where the pitch of endmost electrodes isreduced are shown in FIGS. 8A to 8C. FIG. 8A is a view showing responsesto a touch on an edge point (x=0) of the panel according toEmbodiment 1. The upper diagram of FIG. 8A shows a touch point on thepanel and the lower diagram of FIG. 8A shows response values to thetouch. As shown in the upper diagram of FIG. 8A, the center of thepseudo finger FF is located at an edge (x=0) of the panel. As shown inthe lower diagram of FIG. BA, when the touch point is at x=0,Intersection 4 has a smaller response value than Intersection 4 in thelower diagram of FIG. 7A but Intersection 3 already responds to somedegree. FIG. 8B is a view showing responses to a touch on a point(x=r/2) r/2 distant from an edge of the panel according to Embodiment 1.The upper diagram of FIG. 8B shows a touch point on the panel and thelower diagram of FIG. 8B shows response values to the touch. As shown inthe upper diagram of FIG. 8B, the center of the pseudo finger FF islocated at a near-edge point (x=r/2) of the panel. As shown in the lowerdiagram of FIG. 8B, when the touch point is at x=r/2, Intersection 3already provides a sufficiently significant response value, whichcontributes to the centroid calculation. FIG. 8C is a view showingresponses to a touch on a point (x=r) r distant from an edge of thepanel according to Embodiment 1. The upper diagram of FIG. 8C shows atouch point on the panel and the lower diagram of FIG. 8C shows responsevalues to the touch. As shown in the upper diagram of FIG. 8C, thecenter of the pseudo finger FF is located at a near-edge point (x=r) ofthe panel. As shown in the lower diagram of FIG. 8C, when the touchpoint is at x=r, Intersection 3 provides a sufficiently significantresponse value, which contributes to the coordinate calculation. As seenfrom the above, in the cases where the pitch of endmost electrodes isreduced in the above manners, a change in touch point can be detectedeven when the touch point is at or near x=0. For the above reasons, thecoordinate accuracy in the edge regions of the panel can be improved.

Although the above description has been given taking as an example theendmost Rx electrodes, the same applies to the endmost Tx electrodes.The above improvement in the accuracy of coordinate detection enablesthat when a line or a figure is drawn on the touch panel, the same traceas drawn by a touch, even near the edges of the panel display, is outputwithout distortion.

<Sensitivity Correction>

Since a change in the pitch of the endmost electrodes involves a changein the sensitivity of them, the sensitivity is corrected by softwareduring the coordinate calculation. The sensitivity of a Tx-Rxintersection is roughly proportional to the area of the intersection((Tx pitch)×(Rx pitch)). Therefore, the four corner intersections havethe minimum sensitivity when the pitch of the endmost Tx electrodes andthe pitch of the endmost Rx electrodes are reduced. Even if theirsensitivities are corrected by software, their noise cannot becorrected. Therefore, it is necessary to achieve a satisfactory S/Nratio at the four corner intersections. This condition of the S/N ratiodetermines the limit of reduction of the pitch.

FIG. 9 is a flowchart of the sensitivity correction. First, respectivetouch response values Sij at some Tx-Rx intersections are acquired froman A/D converter (Step S91). Because the correction value forsensitivity varies with the position of the Tx-Rx intersection, it isdetermined where each Tx-Rx intersection is located (Step S92). Thetouch response value at an intersection (i,j) is designated by Sij, thetouch response value corrected in sensitivity is designated by S′ij, thecorrection value for sensitivity in edge regions in the X-direction isdesignated by Ax, the correction value for sensitivity in edge regionsin the Y-direction is designated by Ay, and the correction value forsensitivity at corners is designated by Ac. If there is no touch, Sij=0but Sij is not always zero because of the presence of noise. If theintersection is in either one of the edge regions in the X-direction,S′ij=Sij×Ax (Step S93) where Ax is approximately equal to ((the pitch ofintermediate electrodes in the X-direction)/(the pitch of endmostelectrodes in the X-direction)). If the intersection is in either one ofthe edge regions in the Y-direction, S′ij=Sij×Ay (Step S94) where Ay isapproximately equal to ((the pitch of intermediate electrodes in theY-direction)/(the pitch of endmost electrodes in the Y-direction)). Ifthe intersection is at any one of the corners, S′ij=Sij×Ac (Step S95)where Ac is approximately equal to Ax×Ay. If the intersection is in theintermediate region (non-edge region), S′ij=Sij, i.e., no correction ismade (Step S96). The centroid of the touch response values S′ij at theintersections is calculated to obtain a touch detection coordinate (StepS97). The touch detection coordinate obtained by the centroidcalculation is subjected to an edge correction (Step S98). Thecoordinate subjected to the edge correction as described hereinafter isoutput to a host (Step S99).

<Edge Correction>

FIG. 10A is a diagram for illustrating a peripheral coordinatecorrection according to Comparative Example 1. Where the pitch of theelectrodes in the X-direction is Px, the intersection pitch for use inthe centroid calculation in the ordinary electrode pattern (ComparativeExample 1) is also Px. Where the entire length of the pattern in theX-direction is L, the range of possible touch coordinates resulting froma simple centroid calculation is from Px/2 to L−Px/2. In this case, acorrection is made by converting a coordinate of Px/2 to Px into 0 to Pxand a coordinate of L−Px to L−Px/2 into L−Px to L. This correction isreferred to as an edge correction or a peripheral coordinate correction.

FIG. 10B is a diagram for illustrating a peripheral coordinatecorrection according to Embodiment 1. In the pattern in which the pitchof endmost electrodes is reduced (Embodiment 1), the positions of theendmost intersections are defined so that the intersection pitch for usein the centroid calculation becomes Px. Where the pitch of endmostelectrodes in the X-direction is Pex and the entire length of thepattern in the X-direction is L′, the range of possible touchcoordinates resulting from a simple centroid calculation is fromPex−Px/2 to L′−Pex+Px/2. In this case, a correction is made byconverting a coordinate of Pex−Px/2 to 2(Pex−Px/2) into 0 to 2(Pex−Px/2)and a coordinate of L′−2(Pex+Px/2) to L′−Pex+Px/2 into L′−2(Pex+Px/2) toL′.

Although the above description has been given of an edge correction inthe X-direction, an edge correction in the Y-direction is made in thesame manner.

<Calibration for Each Intersection>

Because calibration values in the panel edge regions are changed by thepitch reduction, a calibration is made for each Tx-Rx intersection.

First, a description will be given of the calibration. FIG. 11 shows anexample of a basic structure of a touch detection circuit (with nocalibration circuit). FIGS. 12A to 12D show examples of waveforms upondetection of a touch. FIG. 12A shows a voltage waveform of a Tx pulse,FIG. 12B shows a current waveform of a coupling current, FIG. 12C showsa voltage waveform of an integrated output, and FIG. 12D shows anenlarged voltage waveform of the integrated output of FIG. 12C. Thetouch detection circuit 51 includes an integrating circuit 52 and ananalog/digital converter circuit (A/D converter circuit or A/Dconverter) 53. The integrating circuit 52 includes an operatingamplifier 54, an integrating capacitor Cint, and a reference voltagesource Vref. When a Tx pulse as shown in FIG. 12A is applied to a Txelectrode, a pulsed coupling current based on a coupling capacitance Cxybetween the Tx electrode and an Rx electrode as shown in FIG. 12B flowsthrough the Rx electrode. This coupling current is converted into avoltage as shown in FIG. 12C by the integrating circuit 52. The outputof the integrating circuit 52 (integrated output) is converted into adigital value by the A/D converter circuit 53. In this manner, a touchis detected by a variation in the coupling capacitance Cxy between Txand Rx electrodes caused by the touch.

However, an amount of variation (ΔCxy) from the coupling capacitance Cxyduring no touch to that during touch is only about 10% to about 20% ofthe coupling capacitance Cxy during no touch as shown in FIG. 12D.Therefore, an appropriate output range for A/D conversion is set byadding an offset to the integrated output. The addition of an offset isreferred to as a calibration of the touch panel and a setting valuedeterminative of an offset is referred to as a calibration value.Specifically, the portion B of the output of FIG. 12D is offset by thecalibration so that the portion A thereof is set as the output range forA/D conversion.

FIG. 13 is a diagram showing a basic structure of a touch detectioncircuit having a calibration function. The touch detection circuit 51 cincludes an integrating circuit 52, an A/D converter circuit 53, and acurrent source 55. The integrating circuit 52 includes an operatingamplifier 54, an integrating capacitor Cint, and a reference voltagesource Vref. In the circuit of FIG. 13, the offset is an integratedvalue of a calibration current. Although FIGS. 11, 12A to 12D, and 13show waveforms of a single Tx pulse, a touch detection is generallyperformed by integrating a plurality of pulses per frame and per Txelectrode.

When the pitch of the endmost electrodes is reduced, Cxy at each oftheir intersections is also reduced roughly in proportion to the area ofthe intersection ((Tx pitch)×(Rx pitch)). In other words, the necessaryoffset differs between the endmost electrodes and the intermediateelectrodes. For this reason, the calibration is made for eachintersection and the resultant calibration value for each intersectionis stored. The calibration is made on the display device beforeshipment. The calibration values are stored in a non-volatile memory,such as an EEPROM or a flash memory, and read at each start-up of thedisplay device.

FIG. 14 is a flowchart of a calibration according to Embodiment 1.First, the calibration value is set at a median (Step S141). Next, adetection operation is executed in a no-touch condition (Step S142).Next, the magnitude of the integrated output voltage Vout is determined,where Vz represents a calibration target voltage for Vout during notouch and ε represents a convergence criterion constant (Step S143). IfVout>Vz+ε, the calibration value is changed to reduce the calibrationcurrent (Step S144). If Vout<Vz−ε, the calibration value is changed toincrease the calibration current (Step S145). If |Vout−Vz|<ε, thecalibration value is settled as it is (Step S146).

While any one of the Tx electrodes is selected and a pulse is applied tothe selected Tx electrode, the Rx electrodes concurrently operate.Therefore, all the Rx electrodes are concurrently calibrated for each Txelectrode. This calibration is made to every Tx electrode.

Embodiment 2

FIG. 15 is a block diagram showing a general structure of a touch paneldevice according to Embodiment 2. A touch panel device 300 of thisembodiment includes a capacitive touch panel 301, a capacitancedetecting section 302, a control section 303, and a bus connectionsignal line 335. An electrode pattern (composed of X electrodes 341 andY electrodes 342) which serves as sensor terminals for detecting auser's touch is formed on the touch panel 301. The X electrodes 341 andY electrodes 342 are connected to the capacitance detecting section 302.The capacitance detecting section 302 is configured to sequentiallyapply a pulse to the X electrodes 341, with the X electrodes 341 astransmitting electrodes (drive electrodes) and the Y electrodes 342 asreceiving electrodes, to measure the interelectrode capacitance (mutualcapacitance) at each electrode intersection. The control section 303 isconfigured to detect a touch based on the above measurement results ofthe respective interelectrode capacitances at the electrodeintersections and notify the host of the detection result via the busconnection signal line 335.

FIG. 16 is a schematic cross-sectional view showing a cross-sectionalstructure of the touch panel in Embodiment 2. The touch panel 301 has astructure in which a substrate layer 323 as a base layer, X electrodes341 and Y electrodes 342, and a protective layer 322 are sequentiallylaid and a surface glass 321 is attached to the top. Needless to say,the touch panel 301 of this embodiment is mounted on a display panel(for example, a liquid crystal display panel or an organic EL displaypanel). FIG. 16 shows a state of electric lines of force when the touchpanel 301 is touched with a finger 360. The finger (a pseudogroundedconductor) 360 functions as a shield to obstruct the electric lines offorce 324. Thus, the interelectrode capacitance value (mutualcapacitance value) between the X electrode 341 and the Y electrode 342decreases.

FIGS. 17A to 17C are views schematically showing plane patterns ofelectrodes of a capacitive external touch panel. For convenience ofdescription, these figures show the case where the touch panel includesseven Y electrodes (transmitting electrodes, Tx electrodes or firstelectrodes) 342 and five X electrodes (receiving electrodes, Rxelectrodes or second electrodes) 341. FIG. 17A shows an ordinaryelectrode pattern (Comparative Example 2), FIG. 17B shows a firstexample of this embodiment where the pitch of the endmost electrodes ischanged from that in the ordinary electrode pattern (the electrodepattern is tailored in edge regions), and FIG. 17C is a second exampleof this embodiment where the pitch of the endmost electrodes is changed(the electrode pattern is proportionally reduced in edge regions).

In Comparative Example 2 of FIG. 17A, all the Tx electrodes 342 haveequal widths and equal spacings and all the Rx electrodes 341 also haveequal widths and equal spacings. The pitch (P_(Tx)) of each Tx electrode342 is the distance between the pair of adjacent horizontal brokenlines. All the pitches (P_(Tx)) of the Tx electrodes 342 are equal. Thepitch (P_(Rx)) of each Rx electrode 341 is the distance between the pairof adjacent vertical broken lines. All the pitches (P_(Rx)) of the Rxelectrodes 341 are equal. Each Tx electrode 342 is located in the middlebetween the pair of adjacent horizontal broken lines, while each Rxelectrode 341 is located in the middle between the pair of adjacentvertical lines.

In the first example of FIG. 17B where the pitch of the endmostelectrodes is changed, the width of the endmost Tx electrodes (Tx1, Tx7)342 ₁, 342 ₇ is smaller than the width of the other Tx electrodes 342and the pitch (P_(Txe)) of the endmost Tx electrodes 342 ₁, 342 ₇ issmaller than the pitch (P_(Tx)) of the other Tx electrodes 342 (i.e.,P_(Txe)<P_(Tx)). Furthermore, the width of the endmost Rx electrodes(Rx1, Rx5) 341 ₁, 341 ₅ is smaller than the width of the other Rxelectrodes 341 and the pitch (P_(Rxe)) of the endmost Rx electrodes 341₁, 341 ₅ is smaller than the pitch (P_(Rx)) of the other Rx electrodes341 (i.e., P_(Rxe)<P_(Rx)). The points where the endmost Tx electrodes(Tx1, Tx7) 342 ₁, 342 ₇ intersect with the Rx electrodes are offset fromthe middle between the pair of adjacent horizontal broken lines towardsthe ends of the intersecting Rx electrodes in the Y-direction. Thepoints where the endmost Rx electrodes (Rx1, Rx5) 341 ₁, 341 ₅ intersectwith the Tx electrodes are offset from the middle between the pair ofadjacent vertical broken lines towards the ends of the intersecting Txelectrodes in the X-direction. In this case, leaving the rhomboidalshape of a portion of the Tx electrode adjoining both of each endmost Rxelectrode (for example, Rx1) and the adjacent Rx electrode (for example,Rx2) unchanged from the rhomboidal shape of other similar portions ofthe same Tx electrode is an ingenuity for avoiding a change ofsensitivity of the Rx electrode (Rx2) next to the endmost Rx electrode(Rx1).

In the second example of FIG. 17C where the pitch of the endmostelectrodes is changed, the pattern of the endmost Tx electrodes and thepattern of the endmost Rx electrodes are proportionally reduced.Although also in FIG. 17C the pitch (P_(Txe)) of the endmost Txelectrodes 342 _(1C), 342 _(7C) and the pitch (P_(Rxe)) of the endmostRX electrodes 341 _(1C), 341 _(5C) are smaller than the pitch of theother Tx electrodes and the pitch of the other Rx electrodes,respectively, FIG. 17C is different from FIG. 17B in the followingpoint: since the regions of the endmost Rx electrodes 341 _(1C), 341_(5C) are proportionally reduced, the distance between the intersectionof each endmost Rx electrode 341 _(1C), 341 _(5C) with each Tx electrodeand the intersection of the adjacent Rx electrode 341 with the same Txelectrode is different from the distance between the other pairs ofadjacent intersections of the Rx electrodes with the same Tx electrode.Since the regions of the endmost Tx electrodes 342 _(1C), 342 _(7C) areproportionally reduced, the width of the endmost Tx electrodes 342_(1C), 342 _(7C) is smaller than the width of the other Tx electrodes342 and each endmost Tx electrode (Tx1, Tx7) 342 _(1C), 342 _(7C) islocated in the middle between the pair of adjacent horizontal brokenlines. Since the regions of the endmost Rx electrodes 341 _(1C), 341_(5C) are proportionally reduced, the width of the endmost Rx electrodes341 _(1C), 341 _(5C) is smaller than the width of the other Rxelectrodes 341 and each endmost Rx electrode (Rx1, Rx5) 341 _(1C), 341_(5C) is located in the middle between the pair of adjacent verticalbroken lines. In this case, the sensitivity of the electrodes next tothe endmost electrodes is slightly reduced but the coordinate accuracycan be effectively improved.

In the cases where the pitch of the endmost electrodes is changed in theabove manners, the coordinate accuracy in the edge regions of the panelcan be improved for the same reasons as Embodiment 1. The aboveimprovement in the accuracy of coordinate detection enables that when aline or a figure is drawn on the touch panel, the same trace as drawn bya touch, even near the edges of the panel display, is output withoutdistortion.

Although the invention made by the inventors has thus far been describedin detail with reference to embodiments, it goes without saying that thepresent invention is not limited to the above embodiments and thus maybe modified in various forms.

What is claimed is:
 1. A touch panel comprising: a plurality of firstelectrodes arranged at predetermined pitches and extending in a firstdirection; and a plurality of second electrodes arranged atpredetermined pitches and extending in a second direction, wherein theplurality of first electrodes and the plurality of second electrodes arearranged so that the first electrodes are overlapped with the secondelectrodes in plan view and spaced from the second electrodes incross-sectional view, both endmost first electrodes of the plurality offirst electrodes have a smaller pitch than the other first electrodes,both endmost second electrodes of the plurality of second electrodeshave a smaller pitch than the other second electrodes and a width thatis the same as the other second electrodes, an endmost second electrodeis offset from the middle of the smaller pitch of the endmost secondelectrode towards an end of a first electrode in the first direction, adetected touch is based on a capacitance variation at one or moreintersections of the plurality of first electrodes with the plurality ofsecond electrodes, each pitch of the plurality of second electrodes is adistance between two vertical imaginary lines, each second electrode ofthe plurality of second electrodes other than the endmost secondelectrodes is in the middle of the distance between the two imaginarylines for every pitch of the plurality of second electrodes other thanthe endmost second electrodes, the endmost second electrodes are offsetfrom the middle of the distance between the two imaginary lines towardsthe ends of intersecting first electrodes in the first direction, andwhen the detected touch is at an edge region in the second direction, acorrection value is applied to the detected touch, and the correctionvalue is approximately equal to the pitch of a second electrode of theplurality of second electrodes other than the endmost second electrodesdivided by the pitch of the endmost second electrode.
 2. The touch panelaccording to claim 1, being configured to calculate a centroid of touchresponse values to obtain a touch coordinate.
 3. The touch panelaccording to claim 1, being configured to apply a corner correctionvalue to the detected touch.
 4. The touch panel according to claim 1,being configured to make a calibration for each of the intersections ofthe plurality of first electrodes with the plurality of secondelectrodes.
 5. The touch panel according to claim 1, wherein portions ofthe first electrodes and the second electrodes not overlapped with eachother in plan view have a rhombic shape.